1. Field of the Invention
The present invention generally relates to a driving method of a light source, in particular, to a driving method of a light source in a backlight apparatus.
2. Description of Related Art
FIG. 1 is a block diagram illustrating the internal circuit of a conventional backlight apparatus. Referring to FIG. 1, the conventional backlight apparatus 100 includes a light source module 110 which is composed of a plurality of light sources 112, such as light emitting diodes (LEDs). The light sources 112 are connected in series, and the last light source is grounded via a resistor 114.
A power supply module 130 may further be disposed in the conventional backlight apparatus 100, wherein the power supply module 130 generates a driving current I1 for driving the light source module 110 according to a feedback voltage of the light source module 110. A switch 140 is disposed between the power supply module 130 and the light source module 110. This switch 140 determines, in accordance with a control signal Vp whether or not to conduct the driving current I1 to the light source module 110 to allow the light source module 110 to emit light.
FIG. 2 is a graph illustrating a curve of the driving current of the light source module in FIG. 1, against time. Referring to both FIG. 1 and FIG. 2, when the switch 140 is turned off, the driving current I1 is not conducted to the light source module 110, so that the light source module 110 is disabled. Here the light source module 110 does not generate any operating current and the power supply module 130 does not detect any feedback signal. Accordingly, the power supply module 130 misjudges that the driving current I1 it outputs is insufficient for driving the light source module 110 and continues to output the driving current I1.
Some energy-storage elements such as capacitors or inductors are usually disposed in the power supply module 130. Thus, when the switch 140 is turned off, the power supply module 130 is still in operation and the driving current I1 it outputs charges these energy-storage elements. When the switch 140 is turned on, the energy-storage elements transiently release the power they have stored, as a result, the quantity of the driving current transiently increases (as the portions enclosed by the dotted line 201 in FIG. 2), and accordingly colour temperature error is caused to the light source module 110 and power is wasted.